The present invention relates to a method and an apparatus for separating a mixture containing carbon dioxide by cryogenic distillation.
For a variant, it relates to the scrubbing of a liquid mixture of CO2 and impurities dissolved by cryogenic distillation, the tank liquid of the distillation column being reboiled and superheated.
The scrubbing of liquid CO2 containing more volatile dissolved impurities is mostly done by cryogenic distillation. For this, the distillation column is fed with liquid CO2 and a part of the liquid in the column tank is vaporized to generate the vapor which will run counter-current to the liquid all along the column. To generate the vapor, a reboiler is most often used: a hot fluid will reheat the liquid to its boiling point to generate the vapor at a temperature as close as possible to its liquid/vapor balance point to improve the distillation in the bottom of the column.
The nature of the hot fluid can vary: a utility (liquid water or steam, electricity, etc.), a fluid from the process, etc. In effect, the heat exchange in the reboiler makes it possible to cool the hot fluid. The exchanged cold can therefore be exploited.
In the case of separation of CO2 by cryogenics (partial condensation, solidification, permeation, etc.), the gas to be scrubbed has to be cooled to enrich the production in CO2. This gas can therefore be cooled against the liquid from the column tank to be distilled in the reboiler. Since the gas often has to be cooled to temperatures lower than the column tank, it will continue to be cooled in another exchanger against another cold fluid, as can be seen in EP-A-1953486.
US-A-2011/029867 illustrates only in the figures a duct making it possible to send tank liquid from the carbon dioxide distillation column to a heat exchanger where the mixture to be separated is cooled. A duct also makes it possible to return a fluid to the column but the document does not specify the state of this fluid.
The percentages relative to the purity in this text are molar percentages.